Direct catalytic conversion of sugars to ethanol

ABSTRACT

Sugars comprising the monosaccharides glucose and fructose, and the disaccharides sucrose and mannose are catalytically converted to ethanol at ambient temperature in a sulfate fortified acid medium in the presence of transition metal compounds possessing a degree of symmetry. This is not a fermentation process but is a catalytic chemical process where conversion efficiency is improved by saturating the acidic reaction mixture with inorganic sulfate salts to reduce competitive reactions. Ethanol formed during the reaction may be removed by distillation, following injection of nitric acid, facilitating a continuous process.

REFERENCES CITED

U.S. Patent Documents Pat. No. Issue Date Author Comments 8,697,406 Apr. 15, 2014 MK Carter Direct catalytic conversion of sugars to ethanol (75° C.-250° C.) 7,070,967 Jul. 4, 2006 MC Dale, Flocculent Saccharomyces M Moelhman cerevisae strain produced ethanol in fermentable sugar or fermentable starch/ enzyme. 6,747,067 Jun. 8, 2004 J. Melnichuk, Steam gasification of KV Kelly cellulose to carbon monoxide and hydrogen, catalytically transformed to methyl alcohol and acetic acid. 6,660,506 Dec. 9, 2003 QA Nguyen, Dilute acid hydrolysis with FA Keller, metal salts converting MP Tucker lingo-cellulose biomass to sugars, then ethanol 4,876,196 Oct. 24, 1989 W Salbrunn, Method of continuously E Steiner, producing ethanol from sugar W Wohrer, by fermentation using O Meixner Zymomonas mobilis at a pH of from 4.5 to 7 4,797,360 Jan. 10, 1989 HW Doelle Conversion of sucrose to fructose and ethanol by fermentation using Zymomonas mobilis and/or the enzyme levansucrase 4,415,749 Nov. 15, 1983 DC Hargis, Catalytic conversion of M Dubeck methanol and synthesis gas WR Pretzer, to ethanol and methyl acetate TP 4,409,404 Oct. 11, 1983 Kobylinski, A catalytic process for JE Bozik production of anhydrosugar alcohol

BACKGROUND

Field of Invention

This invention relates to catalytic chemical conversion of sugars comprising monosaccharides and disaccharides to ethanol at substantial yields in a single process step without fermentation. Specifically, this application discloses rapid, efficient catalytic conversion of sugar materials including sucrose, mannose, glucose, fructose and galactose in an acid medium containing inorganic sulfates comprising alkali metal, alkaline earth and other soluble metal sulfates to ethanol employing catalysts based on transition metal complexes possessing a degree of symmetry as described herein.

Description of Prior Art

The chemical process industry has grown to maturity based on petroleum feed stocks, a non-renewable resource that may become unavailable in the next 100 years. This planet Earth fosters continual growth of abundant carbohydrate based plants including fruits, vegetables, starches, grain food sources, grasses, shrubs, trees and related natural materials. Trees, corn cobs, support plant stalks, reeds and grasses are subject to catalytic digestion processes converting cellulosic materials to sugar substances whereas the present application teaches catalytic conversion of sugars to ethanol. These processes are many times faster and more efficient than fermentation processes. A major industry is blooming in ethanol production and this process is fundamental for efficient catalytic conversion of essentially all sugar materials to ethanol for use as a fuel and as a starting material in a modern chemical process industry.

Previous methods for production of ethanol include Fischer-Tropsch conversion of syntheses gas and fermentation of sugars. Fermentation of cane and beet sugar, grains and corn, as well as fermentation of sugars produced by acid digestion of wood and related plant cellulose materials constitute the majority of present production processes. Significant effort has been expended to isolate specific enzymes that may be more efficient in the fermentation process and those that might increase conversion efficiency well above ten percent. Ethanol has also been made from ethylene dissolved in sulfuric acid, diluted and isolated by distillation and by heating ethylene with steam at 300° C. and 1000 to 4000 psi pressure using acid or acidic transition metal oxide catalysts but these processes are not efficient in direct production of ethanol.

U.S. Pat. No. 4,415,749, issued Nov. 15, 1983, teaches a process converting methanol and synthesis gas to ethanol and methyl acetate in the vapor phase at 225° C. to 300° C. over zero valent Rh and Fe at 50 psig to 250 psig pressure. U.S. Pat. No. 6,747,067, issued Jun. 8, 2004, presents gasification of cellulose to carbon monoxide and hydrogen for subsequent formation of methanol, ethanol and related products. Neither of these processes start with natural sugars and ethanol is not the primary product. Ligno-cellulose biomass has been converted to sugars, then ethanol using metal salts as discussed in U.S. Pat. No. 6,660,506, issue Dec. 9, 2003. There is also a catalytic process for conversion of sugar alcohols to anhydro-sugar alcohols as disclosed in U.S. Pat. No. 4,409,404, issued Oct. 11, 1983.

U.S. Pat. No. 7,070,967, issued Jul. 4, 2006 teaches application of the flocculent strain Saccharomyces cerevisae for conversion of sugar to ethanol by fermentation. U.S. Pat. No. 4,876,196, issued Oct. 24, 1989 discloses a method of continuously producing ethanol from sugar by fermentation using Zymomonas mobilis at a pH of from 4.5 to 7 and U.S. Pat. No. 4,797,360, issued Jan. 10, 1989 offers a process for conversion of sucrose to fructose and ethanol by fermentation using Zymomonas mobilis and/or the enzyme levansucrase. These fermentation processes are slow and do not teach direct catalytic conversion of essentially any sugar to ethanol. Direct catalytic conversion of sugars to ethanol has been conducted in the temperature range of 75° C. to 250° C. as disclosed in U.S. Pat. No. 8,697,406, issued Apr. 15, 2014.

The present application discloses use of low valent mono-metal, di-metal, tri-metal and/or poly-metal backbone or molecular string type transition metal catalysts, as described in this application, for direct production of ethanol from sugar materials in the temperature range of 0° C. to 75° C. Catalytic conversion processes are not limited to a single transition metal compound or catalyst but are effective using a wide range of catalysts.

SUMMARY OF THE INVENTION

This invention describes a chemical process using selected members of transition metal catalysts possessing a high degree of symmetry in their lower valence states for catalytic conversion of sugar materials to ethanol. This process is rapid and direct in that sugars are placed into solution with the catalytic acid medium at reaction conditions and ethanol is soon produced. Fermentation is not required.

It is an object of this invention, therefore, to provide a catalytic process facilitating conversion of sugar materials to ethyl alcohol in a sulfate fortified acid digestion medium. It is another object of this invention to catalytically convert sugar materials to ethanol at normal solvent vapor pressure. It is still another object of this invention to catalytically convert sugar materials to ethanol at ambient temperature. Other objects of this invention will be apparent from the detailed description thereof which follows, and from the claims.

DETAILED DESCRIPTION OF THE INVENTION

A process for catalytic chemical conversion of sugar materials comprising monosaccharides, including glucose and fructose, and disaccharides, including sucrose and mannose, to ethanol is taught. The process for conversion of sugar materials to ethanol uses no fermentation and is conducted in a sulfate fortified acid medium using transition metal compounds, such as [vanadium]₂, [manganese]₂ or [cobalt]₂ compounds, for which the transition metals and directly attached atoms possess C_(4v), D_(4h) or D_(2d) point group symmetry. These catalysts have been designed based on a formal theory of catalysis, and the catalysts have been produced, and tested to prove their activity. The theory of catalysis rests upon a requirement that a catalyst possess a single metal atom or a molecular string such that transitions from one molecular electronic configuration to another be barrier free so reactants may proceed freely to products as driven by thermodynamic considerations. Catalysts effective for chemical conversion of sugars to ethanol can be made from mono-metal, di-metal, tri-metal and/or poly-metal backbone or molecular string type compounds of the transition metals comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold or combinations thereof. These catalysts are typically made in the absence of oxygen so as to produce compounds wherein the oxidation state of the transition metal is low, typically monovalent, divalent or trivalent. Anions employed for these catalysts comprise fluoride, chloride, bromide, iodide, cyanide, isocyanate, thiocyanate, sulfate, phosphate, oxide, hydroxide, oxalate, acetate, organic chelating agents and/or more complex groups. Mixed transition metal compounds have also been found to be effective catalysts for some chemical conversions.

These catalysts act on glucose, fructose, sucrose, mannose and essentially any sugar type carbohydrate compound to generate free radicals in times believed to be the order of or less than that of a normal molecular vibration. This may be viewed as generation of free radical reactants in equilibrium such that the reaction indicated by the equation C₆H₁₂O₆→2CH₃CH₂OH+2CO₂ may proceed. Water provided in the acid solvent reaction sphere causes hydrolysis of the disaccharides such that catalytic exposure of resulting monosaccharides to monomer, dimer or oligomer transition metal compounds produces ethanol and carbon dioxide. Thus, ethanol is the product of catalytic conversion and the carbon dioxide by product is released during the process. Fortifying the acid medium with inorganic sulfates essentially saturates the solvent and reduces the tendency to form known by products.

Catalyst Selection Considerations

A Concepts of Catalysis effort formed a basis for selecting molecular catalysts for specified chemical reactions through computational methods by means of the following six process steps. An acceptable chemical conversion mechanism, involving a single or pair of transition metal atoms, was established for the reactants (step 1). A specific transition metal, such as cobalt, was selected as a possible catalytic site as found in an M or M-M string (step 2), bonded with reactant molecules in essentially a C_(4v), D_(2d) or D_(4h) point group symmetry configuration (transition metal and directly bonded atoms only), and having a computed bonding energy to the associated reactants of 0>E>−60 kcal/mol (step 3). The first valence state for which the energy values were two-fold degenerate was 2+ in most cases although other valence states are possible (step 4). Sulfate, chloride and other anions may be chosen provided they are chemically compatible with the metal in formation of the catalyst (step 5). An inspection of the designed catalyst should also be conducted to establish compliance with the rule of 18 (or 32) to stabilize the catalyst; thus, compatible ligands may be added to complete the coordination shell (step 6). This same process may be applied for selection of a catalyst using any of the first, second or third row transition metals, however, only those with acceptable negative bonding energies can produce effective catalysts. The approximate relative bonding energy values may be computed using a semi-empirical algorithm or other means. Such a computational method indicated that most of the first row transition metal complexes may be anticipated to produce usable catalysts once the outer coordination shell had been completed with ligands. In general, preliminary energy values computed for transition metal carbohydrate complexes are indicated to produce useable catalysts once bonding ligands have been added.

Catalyst structures commonly including a pair of bonded transition metal atoms require chelating ligands and/or bonding orbital structures that may be the same for both metals. The following compounds comprise a limited selection of examples. For the first row transition metals vanadium catalysts comprise vanadium (II) oxide, (VO)₂, and (VF₂)₂ having V—V bonds and ethylenediamine (EDA) links the metals in (VCl₂)₂(EDA)₂, ethanol or other reactants may displace a CO and/or a THF in the compound [V(THF)₄Cl₂][V(CO)₆]₂ while V₂(SO₄)₃ may also be useful. Chromium catalysts comprise Cr(O₂CCH₃)₂(HO₂CCH₃)₂, Cr₂[CH₃(C₅H₃N)O]₄, (CrCl₂)₂.2EDA, (CrBr₂)₂(EDA)₂, [Cr(OH)₂]₂(EDA)₂ and Cr₂(O₂CCH₃)₄(H₂O)₂ where a reactant may displace waters of hydration. Manganese catalysts comprise [Mn(diethyldithiocarbamate)]_(n), (MnCl₂)₂(EDA)₂, K₂[Mn₂Cl₆(H₂O)₄] and Mn₂(C₅H₈O₂)₄(H₂O)₂. Iron catalysts comprise (FeCl₂)₂(EDA)₂, (FeBr₂)₂(EDA)₂ and Fe₂(SO₄)₂. Cobalt catalysts comprise Co₂(C₆H₅O₂)₂(C₆H₆O₂)₂, Co₂(C₅H₈O₂)₄(H₂O)₂, Co(C₆H₅O₂)₂(C₆H₆O₂)₂, Co₂(C₆H₅O₂)₄, Ca₃[Co₂(CN)₁₀]13H₂O, [Co(CN)₂]₂K₃Cu(CN)₄ and Co₂(SO₄)₂. Nickel catalysts comprise Ni₂(C₆H₅N₃C₆H₅), Ni₂Br₂(C₈H₆N₂) and Ni₂S₂(C₂H₂C₆H₅). Copper catalysts comprise [CuO₂CC₆H₅]₄, [CuO₂CCH₃]₄, (CuCl)₂(EtOH)₄, (CuCN)₂(EtOH)₄ and K₂Cu₄(μ₂SC₆H₅)₆.

Second and third row transition metals are organized in groups or pairs. Zirconium, hafnium, nobelium and tantalum comprise (ZrCl₂)₂, (HfCl₂)₂, (HfF₂)₂, (NbCl₂)₂, (TaCl₂)₂ and (TaF₂)₂. Molybdenum and tungsten catalysts comprise [Mo(CO)₄Cl₂]₂, [W(CO)₄Cl₂]₂, [K₄MoCl₆]₂, [Mo(CN)₂]₂K₃Cu(CN)₄, [W(CN)₂]₂K₃Cu(CN)₄, [Mo(Cl)₂]₂K₃Cu(CN)₄ and [W(Cl)₂]₂K₃Cu(CN)₄. Rhenium and technetium catalysts comprise [Re(CO)₂Cl₂(PR₃)₃]₂ and [Tc(CO)₂Cl₂(PR₃)₃]₂. Platinum, palladium, ruthenium, rhodium, osmium and iridium catalysts comprise (PtF₂)₂, (PdF₂)₂, [RuCl₂]₂(EDA)₄, [RhCl₂]₂(EDA)₄, [Ru(C₈H₆N₂)₂Cl₂]₂, [Rh(C₈H₆N₂)₂Cl₂]₂, Ru₂(O₂CR)₄Cl, Rh₂(O₂CR)₄Cl, [PdCl₄(PBu₃)₂]₂, [PtCl₄(PBu₃)₂]₂, [OsCl₂]₂(EDA)₄ and [IrCl₂]₂(EDA)₄. Silver and gold catalysts comprise (AgCN)₂K₃Cu(CN)₄ and (AuCN)₂K₃Cu(CN)₄.

A limited number of single transition metal atom catalyst complexes containing four ligands each belong to the required point group symmetry, although typically these compounds form associated molecular pairs. These catalysts comprise M(II)(C₆H₅O₂)₂(C₆H₆O₂)₂, M(II)(p-C₆H₅O₂)₂, M(II)(C₆H₆NO)₂(C₆H₇NO)₂ and M(II)(O₂CCH₃)₂(HO₂CCH₃)₂ plus possible solvation ligands where M represents titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum or gold. In a limited number of complexes the transition metal atom may be mono-valent or tri-valent.

Description of Catalyst Preparation and Chemical Conversion

Catalyst preparation may be conducted using nitrogen purging and/or nitrogen blanketing to minimize or eliminate air oxidation of the transition metal compounds during preparation. Transition metal catalysts effective for conversion of sugar materials can be produced by combining transition metal salts in their lowest standard oxidation states with other reactants. Thus, such transition metal catalysts can be made by partially reacting transition metal (I or II) chlorides, bromides, sulfates, cyanides or similar compounds with transition metal (I, II or III) compounds and chelates or by forming transition metal compounds in a reduced state by similar means where di-, tri- and/or poly-metal compounds result. A number of [M(II) sulfate]₂ catalysts form by simply adding a transition metal (II) salt to an acid sulfate medium. Some alternate examples follow.

Example 1

The CoSO₄ catalyst was prepared in a nitrogen atmosphere by addition of 0.536 gram (2 mmol) of sodium sulfate to 0.498 gram (2 mmol) of cobalt (II) acetate tetrahydrate dispersed in 6 mL of nitrogen purged water with mixing and heating. A soluble colored product solution formed. The dissolved catalyst was isolated for use.

Example 2

The MnSO₄ catalyst was prepared in a nitrogen atmosphere by addition of 0.804 grams (3 mmol) of sodium sulfate to 0.533 grams (2 mmol) of manganese chloride tetrahydrate dispersed in 5 mL of nitrogen purged water with mixing and heating. A soluble colored product solution formed. The dissolved catalyst was isolated for use.

Example 3

The compound [V(OSO₄)]₂ was prepared as described by dispersing 1.82 grams of vanadium pentoxide in 10 grams of pure water, dissolving 3.08 grams of ammonium acetate and 4.48 grams of concentrated sulfuric acid. This liquid was gently purged with nitrogen gas to displace dissolved oxygen and 6.5 grams of zinc dust was added in portions during a 5 minute period. The dispersion changed to a colored solution as the catalyst formed.

Chemical Conversion to Ethanol

Sugar material conversions were conducted in an inorganic sulfate fortified dilute sulfuric acid medium by mixing glucose and other sugars in an open reactor with a small amount of catalyst at a temperature in the range of 0° C. to 75° C. Fermentation processes were not employed. A table of ethanol concentration measurements follows.

Ethanol Concentrations Measured for Examples A through I Temperature Reaction Time Glucose to Ethanol Example Reactant (° C.) (minutes) Conversion (%) A Glucose 6 3 74 A ″ 6 10 76 B ″ 22 3 98 B ″ 22 10 98 C ″ 40 3 98 C ″ 40 10 100 D ″ 58 3 98 D ″ 62 10 93 E ″ 75 3 91 E ″ 75 10 97 F Fructose 21 3 84 F ″ 21 10 85 G Sucrose 21 3 96 G ″ 21 10 96 H ″ 58 3 98 H ″ 58 10 102 I Glucose 22 3 98 I ″ 22 10 98

Example A

Dissolved in a 40 mL glass vial were 0.02 gram of potassium sulfate, 0.50 gram of sodium sulfate, 1.71 grams of zinc sulfate, 0.0065 gram of manganese sulfate monohydrate catalyst, 4.00 grams of water (as ice) and 2.92 grams of sulfuric acid. The vial was brought to reaction temperature and 0.90 grams of glucose was dissolved therein. The glass vial was immersed at 6° C. in an ice bath. Analysis samples, 0.10 mL, were withdrawn at 3 minutes and 10 minutes then analyzed for ethanol content, refer to table of results.

Example B

Dissolved in a 40 mL glass vial were 0.62 gram of potassium sulfate, 1.06 grams of sodium sulfate, 0.64 gram of lithium sulfate catalyst, 0.0009 gram of cobalt sulfate catalyst and 0.0123 gram of copper (I) chloride in 4.00 grams of water (as ice) and 2.92 grams of sulfuric acid. The vial was brought to reaction temperature and 0.90 grams of glucose was dissolved therein. The glass vial stood at 22° C. on the laboratory bench. Analysis samples, 0.10 mL, were withdrawn at 3 minutes and 10 minutes then analyzed for ethanol content, refer to table of results.

Example C

Dissolved in a 40 mL glass vial were 1.70 grams of rubidium sulfate, 1.20 grams of magnesium sulfate, 0.0026 gram of manganese sulfate catalyst, 4.00 grams of water (as ice) and 2.92 grams of sulfuric acid. The vial was brought to reaction temperature and 0.90 grams of glucose was dissolved therein. The glass vial was immersed at 40° C. in propylene glycol heating bath. Analysis samples, 0.10 mL, were withdrawn at 3 minutes and 10 minutes then analyzed for ethanol content, refer to table of results.

Example D

Dissolved in a 40 mL glass vial were 0.62 gram of potassium sulfate, 1.06 grams of sodium sulfate, 0.64 gram of lithium sulfate catalyst, 0.0009 gram of cobalt sulfate catalyst and 0.0105 gram of copper (I) chloride in 4.00 grams of water (as ice) and 2.92 grams of sulfuric acid. The vial was brought to reaction temperature and 0.90 grams of glucose was dissolved therein. The glass vial was immersed at 58° C. to 62° C. in propylene glycol heating bath. Analysis samples, 0.10 mL, were withdrawn at 3 minutes and 10 minutes then analyzed for ethanol content, refer to table of results.

Example E

Dissolved in a 40 mL glass vial were 0.02 gram of potassium sulfate, 0.50 gram of sodium sulfate, 1.71 grams of zinc sulfate, 0.0104 gram of manganese sulfate monohydrate catalyst, 0.0104 gram of copper (I) chloride, 4.00 grams of water (as ice) and 2.92 grams of sulfuric acid. The vial was brought to reaction temperature and 0.90 grams of glucose was dissolved therein. The glass vial was immersed at 75° C. in propylene glycol heating bath. Analysis samples, 0.10 mL, were withdrawn at 3 minutes and 10 minutes then analyzed for ethanol content, refer to table of results.

Example F

Dissolved in a 40 mL glass vial were 0.62 gram of potassium sulfate, 1.06 grams of sodium sulfate, 0.64 gram of lithium sulfate catalyst, 0.0018 gram of cobalt sulfate catalyst and 0.0145 gram of copper (I) chloride in 4.00 grams of water (as ice) and 2.92 grams of sulfuric acid. The vial was brought to reaction temperature and 0.90 grams of fructose was dissolved therein. The glass vial stood at 21° C. on the laboratory bench. Analysis samples, 0.10 mL, were withdrawn at 3 minutes and 10 minutes then analyzed for ethanol content, refer to table of results.

Example G

Dissolved in a 40 mL glass vial were 0.62 gram of potassium sulfate, 1.06 grams of sodium sulfate, 0.64 gram of lithium sulfate, 1 drop of vanadium sulfate catalyst solution in 4.00 grams of water (as ice) and 2.92 grams of sulfuric acid. The vial was brought to reaction temperature and 0.90 grams of sucrose was dissolved therein. The glass vial stood at 21° C. on the laboratory bench. Analysis samples, 0.10 mL, were withdrawn at 3 minutes and 10 minutes then analyzed for ethanol content, refer to table of results.

Example H

Dissolved in a 40 mL glass vial were 0.02 gram of potassium sulfate, 0.50 gram of sodium sulfate, 1.71 grams of zinc sulfate, 0.0104 gram of cobalt sulfate catalyst, 0.0122 gram of copper chloride, 4.00 grams of water (as ice) and 2.92 grams of sulfuric acid. The vial was brought to reaction temperature and 0.90 grams of sucrose was dissolved therein. The glass vial was immersed at 58° C. in propylene glycol heating bath. Analysis samples, 0.10 mL, were withdrawn at 3 minutes and 10 minutes then analyzed for ethanol content, refer to table of results.

Example I

Dissolved in a 40 mL glass vial were 0.02 gram of potassium sulfate, 0.50 gram of sodium sulfate, 1.71 grams of zinc sulfate, 0.0065 gram of manganese sulfate monohydrate catalyst, 4.00 grams of water (as ice) and 1.00 gram of sulfuric acid. The vial was brought to reaction temperature and 0.90 grams of glucose was dissolved therein. The glass vial stood at 22° C. on the laboratory bench. Analysis samples, 0.10 mL, were withdrawn at 3 minutes and 10 minutes then analyzed for ethanol content, refer to table of results. 

What is claimed is:
 1. Direct catalytic chemical conversion of sugar materials comprising monosaccharides selected from glucose and fructose, and disaccharides selected from sucrose and mannose, to ethanol in an acid medium containing 0.1 percent to 80 percent metal sulfates at 0° C. to 70° C.
 2. Direct catalytic chemical conversion of sugar materials comprising monosaccharides selected from glucose and fructose, and disaccharides selected from sucrose and mannose, to ethanol in an acid medium containing 0.1 percent to 80 percent metal sulfates at 0° C. to 70° C. wherein catalysts possessing a degree of symmetry are formed from transition metal compounds comprising titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold or combinations thereof. 